The present invention relates to a dot character display apparatus and, more particularly, to a dot character display apparatus for displaying a complex character having a character body and a symbol added over and/or under this character body in a dot matrix display section as a dot pattern.
Generally, in dot character display apparatuses, the internal memory section is provided with character generators for generating a plurality of dot patterns each of which corresponds to each character to be displayed. For example, when character codes indicative of the characters to be displayed are inputted from an external host computer, respective bit data of the relevant dot pattern is read out from the character generators by these character codes and temporarily stored into an image buffer. Thereafter, the respective bit data stored in this image buffer is sequentially read out and respective dot display elements in the dot matrix display section are selectively activated by a matrix drive circuit in accordance with the bit data read out. Thus, the corresponding characters are displayed in the dot matrix display section.
In such a dot character display apparatus, a complex character such as "A" consisting of a character body and a symbol such as umlaut " " or the like added over the character body, as shown in FIG. 1(A), or a complex character such as "A" consisting of a character body and a symbol such as underline " " or the like added under the character body, as shown in FIG. 2(A) are not set in the character generators since it is necessary to minimize the memory capacity. To constitute those complex characters, the data indicative of the character main bodies such as "A" and the like, the data indicative of the upper symbols such as " ", " ", " ", " ", and the like, and the data representative of the lower symbols such as " " and the like are separately stored, respectively. For example, in the case of displaying a complex character of "A", as shown in FIG. 1(B), the bit data of the dot pattern of character body "A" is read out from the first character generator, the bit data of the dot pattern of the upper symbol " " is read out from the second character generator, and the bit data indicative of "A" and " " read out are synthesized in the image buffer. On the other hand, in the case of displaying a complex character of "A", as shown in FIG. 2(B), the bit data of the dot pattern of "A" is read out from the first character generator, the bit data of the dot pattern of " " is read out from the third character generator, and the bit data read out from the first and third character generators are synthesized in the image buffer.
In general, the fundamental unit (one byte) of the data which is stored in the character generators consists of eight bits. For example, the data in the first character generator to store the dot patterns of character bodies is constituted by eight bits as a fundamental unit (one byte). The data in the second and third character generators to store the dot patterns of upper and lower symbols is constituted by four bits, respectively. The two 4-bit data from the second and third character generators are added to constitute 8-bit data.
FIG. 3 is a diagrammatical view showing a transfer state of bit data in a conventional dot character display apparatus. This dot character display apparatus includes first, second, and third character generators CG.sub.1 to CG.sub.3 ; 8-bit A- and B-registers RA and RB; a 16-bit image buffer IB having two 8-bit buffers; and a dot matrix display section DMD which is driven by a matrix drive circuit. For simplicity of explanation, this diagram shows the case where the bit data of one column is generated from the character generators and the dot matrix display section selectively energizes dot display elements of one column in accordance with this bit data.
In such a dot character display apparatus, when character code data is inputted from the outside, processes of the input character code data are executed in accordance with a flowchart of FIG. 4. First, in the case where the input character code data is the complex character code, the corresponding dot pattern is read out from second character generator CG.sub.2 to store the dot pattern of upper symbol on the basis of the code indicative of the upper symbol of this complex character. The bit data at first to fourth bit positions B.sub.1 to B.sub.4 of each column of the dot pattern is stored at first to fourth bit positions B.sub.1 to B.sub.4 of A-register RA, respectively. Next, in accordance with the code representative of the character body included in the input character code data, the dot pattern of the corresponding character body is read out from the first character generator CG.sub.1. The bit data at first to fourth bit positions B.sub.1 to B.sub.4 of the relevant column of the dot pattern is stored at the fifth to eighth bit positions of A-register RA. Further, the remaining bit data, namely, the bit data at the fifth to eighth bit positions B.sub.5 to B.sub.8, of the relevant column of the corresponding dot pattern generated from first character generator CG.sub.1 is stored at the first to fourth bit positions in B register RB. After the bit data corresponding to the character body has been completely stored into A- and B-registers RA and RB, the relevant dot pattern is read out from third character generator CG.sub.3 in accordance with the code indicative of the symbol added under the character body and is stored as lower symbol dot pattern. The bit data at first to fourth bit positions B.sub.1 to B.sub.4 of the dot pattern is read out and stored at the fifth to eighth bit positions of B-register RB.
After completion of storage of the respective bit data into A- and B-registers RA and RB, the respective bit data stored at the first to eighth bit positions of A-register RA is stored at the first to eighth bit positions of the image buffer. The bit data at the first to eighth bit positions of B-register RB is stored at the ninth to sixteenth bit positions of the image buffer. Thereafter, the bit data stored at the first to sixteenth bit positions of the image buffer is sent to the matrix drive circuit. The respective dot display elements of one column in the dot matrix display section are selectively energized by the matrix drive circuit. The same operation is effected for the bit data in succeeding columns of the dot pattern.
On the other hand, if the input character code data is ordinary character code instead of complex character code, it is sufficient to read out the data from only the first character generator to store the dot pattern of character body.
In the dot character display apparatus constituted as described above, each character generator and each register fundamentally handles the 8-bit data. In addition, as shown in FIG. 3, the first to sixteenth bit positions of the image buffer directly correspond to the sixteen nodes of the matrix drive circuit to energize the dot display elements on each column of the matrix display section. Therefore, in the case of displaying the character body of the complex character, it is necessary to separate each column of the dot pattern generated from first character generator CG.sub.1 into upper 4-bit data and lower 4-bit data and then to store the upper and lower 4-bit data into the lower 4-bit positions of the A-register and upper 4-bit positions of the B-register, respectively.
Therefore, it is necessary to use two registers to process the respective bit data of the dot pattern of the character body read out separately from first character generator CG.sub.1. Further, the control program for processing the respective bit data of the dot pattern read out becomes complicated and the data processing time increases.